I collect Swedish Mausers and also have a Ruger 77MkII and a TCR 87 in the 6.5 Swede. It's is one of my favorite cartridges (probably a 3 -way tie between the .308, '06, and the Swede). I have a close friend in Sweden who I visit regularly and he has often suggested that perhaps he could arrange for me to participate in a "hunting party" and hunt moose there. It sounds like a great idea, but I have never seriously considered it as I don't get enough hunting time in the good old USA, and I'd rather exploit the opportunites here (and keep that meat) before going overseas to hunt. Also, to be honest, I do believe it would cause some real marital fireworks if I tried to pull that one off. Finally, hunting to me is an activity that I don't want to do according to "group rules".
Nonetheless, I think there are some differences in the way the Swedes hunt that seemingly contribute to the apparent effectiveness of a given cartridge. I believe that they take some marksmanship (including a moving target) tests prior to qualifying for a hunting license, and their hunting "ettiquette" is far more reserved than ours in general. Multiple shots are rather looked down upon, wounded game, lost meat are serious transgressions, or at least social disgraces. Also, they do hunt in "parties" from stands, and use radios. (So there are very critical witnesses to sloppy shooting.) I suspect that these things have an influence on the overall success rate of the 6.5 cartridge, as opposed to our generally more "freestyle" methods. They should, anyway, I think.
That said, would I hunt moose with a 6.5 in the US or Canada? Absolutely. But like CH says - it would fall in line after my '06.